Polymerization of propylene is carried out in presence of catalyst system consisting of titanium supported on magnesium dichloride (Ziegler Natta) carrying internal donor, an organo aluminium co-catalyst and an external electron donor. Type of internal donor used in pro-catalyst synthesis governs type of external donor to be used during polymerization process along with the co-catalyst.
Diesters and monoesters based catalyst are well known and often used for polymerization of propylene. Diester catalyst systems along with silane as external donor are not self extinguishing in nature which is critical for fluidized bed gas phase polymerization. This means activity of catalyst increases with increasing polymerization temperature leading to lump formation in reactor. Recently oxygen containing kinetics modifier mixtures along with silane are used which controls the activity of catalyst system. However, there is further scope to improve the kinetics control of diester catalyst system using new class of kinetics modifiers.
The molecular weight distribution of polypropylene produced using diester catalyst with silane as external donor is narrow compared to the molecular weight distribution of polypropylene produced using monoester catalyst system. It is desirable to have broad molecular weight distribution for a few applications like BOPP or injection molding homo grades. Therefore, it is desired to have a catalyst system which produces broad molecular weight distribution at similar sterospecificity and melt flow index level for diester catalyst systems along with controlled kinetics of polymerization. Monoester catalyst systems have low to medium polymerization activity with inherent self extinguishing characteristics. Oxygen containing external donors are widely used for polymerization of propylene for monester catalyst. It is also desirable to find new type of external donor system for monoester catalyst.
US 2009/0118115A1 discloses the use of oxygen containing external donors as polymerization kinetics modifiers with silane for controlling the kinetics of polymerization in diester catalyst system. US20060270811A1, US20050277749A1, US20050277569A1, US20050043494A1 disclose use of PMDETA as a ligand for bimetallic catalyst composition which is quite different as compared to the magnesium dichloride supported Titanium catalyst (ZN) system. US20060252894A1 teaches the use of tetra methyl ethylene diamine as one of the internal donors but with a different novelty. U.S. Pat. No. 5,854,164 discloses the use of cyclic organic nitrogen containing external donor such as derivatives of piperidine, pyrolidine, amines, amides etc for polymerization of propylene using monoester catalyst system, however the claimed compound has not been, studied with monoester catalyst system.
Thus, there is need to develop a new class of external donors for diester as well as monoester catalyst system which provides advantage in product characteristics.